The disclosure of Japanese Patent Application No. 2000-233330 filed on Aug. 1, 2000 is incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a driving force transmission device, more particularly, to such a device that is arranged between two shafts and is able to connect/disconnect the shafts transmittable driving force therebetween.
2. Description of the Related Art
As an example of the related art, a driving force transmission device as followings is known. The driving force transmission device consists of a main clutch mechanism, an electromagnetic type pilot clutch and a cam mechanism, which are arranged between a outer case and an inner shaft coaxially and rotatably supported in the outer case. At the driving force transmission device, operating force output from the pilot clutch is amplified by the cam mechanism and transmitted to the main clutch mechanism, so that the main clutch mechanism is operated. As a result, the outer case and the inner shaft are connected to be able to transmit torque.
In the aforementioned driving force transmission device of the related art, the pilot clutch consists of an electromagnet, an armature and a friction clutch. When current is applied to an electromagnetic coil of the electromagnet, magnetic flux is established around the electromagnet through the friction clutch and the armature. As a result, the armature is attracted toward electromagnet so that the friction clutch is engaged. Then the cam mechanism is operated by friction engaging force of the friction clutch, whereby the main clutch mechanism is engaged.
Since the friction engaging force of the friction clutch is controlled according to current quantity applying to the electromagnetic coil of the electromagnet, it is required to control correctly the friction engaging force that leakage of the magnetic flux from the outer case possibly can be prevented. As one of the means to prevent the leakage of the magnetic flux, a non-magnetic substance such as aluminum alloy is used for a material of the outer case.
However, axial spline to connect the outer case with an output shaft are needed for mounting the driving force transmission device on a vehicle. When a flange formed the axial spline cannot be attached with the outer case because of space restriction, an outer case that is made of steel such as S15C and integrally formed the axial spline should be adapted. In a case of adapting the steel outer case, an intermediate portion of the steel outer case is formed by nonmagnetic substance such as stainless steel to prevent the leakage of the magnetic flux. Such a special forming as integrally forming of steel and stainless brings difficult operations of forming and high costs.
In view of the foregoing, an object of the present invention is to prevent the above mentioned problems, namely to prevent the leakage of the magnetic flux through the outer case and control an operation of the pilot clutch correctly even if an outer case is made of only steel.
In order to achieve the above object, the present invention provides a driving force transmission device, which transmits driving force between two rotary members. The driving force transmission device comprises: an outer case; an inner shaft; a main clutch mechanism; an electromagnetic type pilot clutch mechanism; and a cam mechanism. The outer case is connected to the one rotary member and made of magnetic substance. The inner shaft is connected to the other rotary member and arranged into the outer case. The main clutch mechanism transmits driving force between the outer case and the inner shaft. The electromagnetic type pilot clutch mechanism controls operation of the main clutch mechanism, and comprises an electromagnet, an armature and a friction clutch. The cam mechanism amplifies output of the pilot clutch mechanism and transmits amplified output to the main clutch mechanism.
According to a first aspect of the present invention, the driving force transmission device further comprises a first regulating member, which adjusts a clearance between the cam mechanism and the armature to be more than a predetermined distance, and is made of nonmagnetic substance.
Since the clearance between the armature of the pilot clutch mechanism and the cam mechanism is kept more than the predetermined distance to dispose the first regulator, leakage of the magnetic flux through the outer case is avoid even if the outer case is made of steel. Therefore, failures of the attracting the armature that are caused by the leakage of the magnetic flux can be avoided so that the pilot clutch mechanism is maintained to operate well.
According to a second aspect of the present invention, the driving force transmission device further comprises a second regulating member, which adjusts an axial position of the friction clutch.
Since the axial position of the friction clutch is adjusted to push outer and inner clutch plates consisted the friction clutch each other, each distance between the outer clutch plates and the inner clutch plates is adjusted correctly. Therefore, failures of the attracting the armature that is caused by variations of clearances between the outer clutch plates and the inner clutch plates can be avoided.